Universal clamping mechanism

ABSTRACT

A method is provided for processing a lead frame. Generally, a first surface of a lead frame base tape is placed on a first surface of the lead frame. A second surface of the lead frame base tape is placed on a first surface of a porous block. A vacuum is placed on a second surface of the porous block. A device for processing lead frames comprises a porous block with a first side and a second side, and a vacuum system connected to the first side of the porous block. The device may also include devices for attaching chips to the lead frame and wire bonding the chips to the lead frame.

FIELD OF THE INVENTION

The present invention relates generally to integrated circuit packages.More specifically, the invention relates to the clamping of lead framesduring the manufacturing of a Leadless Leadframe Package.

BACKGROUND OF THE INVENTION

An integrated circuit (IC) package encapsulates an IC chip (die) in aprotective casing and may also provide power and signal distributionbetween the IC chip and an external printed circuit board (PCB). An ICpackage may use a metal lead frame to provide electrical paths for thatdistribution. During the process of die attach and wire bonding forconventional semiconductor packages, the semiconductor lead frame orsubstrate material rests on a base block during the epoxy dispensing,die attaching, and wire bonding processes. During these processes theframe or substrate needs to be held down firmly to a heater block by avacuum, a clamp, or both.

To facilitate discussion, FIG. 1 is a top view of a lead frame panel 100made up for a plurality of lead frames that may be used in the priorart. The lead frame may comprise leads 108, die attach pads 112, ties116 for supporting the die attach pads 112 and leads 108, and a skirt120 for supporting the plurality of leads 108 and ties 116. The leadframe panel 100 may be etched or stamped from a thin sheet of metal.FIG. 2 is a cross sectional view of the lead frame panel 100 shown inFIG. 1, along cut lines 2—2, attached to a lead frame base tape 204,which is mounted on a base block 208 used in the prior art. The baseblock 208 has a plurality of holes 212, through which a vacuum isapplied to the lead frame base tape 204 to hold the lead frame 100 andthe lead frame base tape 204 to the base block 208. A top clamp 216 mayalso be used to hold the lead frame 100 and lead frame base tape 204 tothe base block 208. Preferably, the holes 212 are positioned at the dieattach pads 112, not between the die attach pads 112 and the ties 116 orat the ties 116. As a result, a base block with a configuration of holesfor one type of lead frame may not be useful in clamping another type oflead frame.

FIG. 3 is a cross sectional view of another type of lead frame 300mounted on the base block 208 that is used in FIG. 2. Tape 304 is placedacross the leads, die attach pads 312, the ties 308, and skirt 320 ofthe lead frame 300. The tape 304 and lead frame 300 are placed on thebase block 208. Two vacuum holes 212 are under parts of the tape 304connected to die attach pads 312 and two vacuum holes 212 are under tape304 that is next to a gap between a lead 308 and a die attach pad 312.Placing a lead 308 or gap over a vacuum hole 212 may cause the leadframe to float or bounce during the wire bonding process. As a result,the vacuum provided through the base block 208, even in combination witha clamping 316 may not be sufficient to secure the lead frame during thewire bonding and die attach process.

It is desirable to provide a universal base block that is able to securedifferent lead frame configurations.

SUMMARY OF THE INVENTION

To achieve the foregoing and other objects and in accordance with thepurpose of the present invention, a variety of techniques is providedfor processing a lead frame. Generally, a first surface of a lead framebase tape is placed on a first surface of the lead frame. A secondsurface of the lead frame base tape is placed on a first surface of aporous block. A vacuum is placed on a second surface of the porousblock.

Another aspect of the invention provides a device for processing leadframes, comprising a porous block with a first side and a second side,and a vacuum system connected to the first side of the porous block.

These and other features of the present invention will be described inmore detail below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a plan view of a lead frame and die assembly used in the priorart.

FIG. 2 is a cross sectional view of the lead frame panel shown in FIG.1, along cut lines 2—2, attached to a lead frame base tape, which ismounted on a prior art base block.

FIG. 3 is a cross sectional view of another type of lead frame mountedon the prior art base block that is used in FIG. 2.

FIG. 4 is a top view of a base block used in a preferred embodiment ofthe invention.

FIG. 5 is an enlarged view of part of the frame and porous block, shownin FIG. 4.

FIG. 6 is a cross-sectional schematic view of the base block being usedin a die attach and wire bonding device.

FIG. 7 is an enlarged cross-sectional view of part of the base blockshown in FIG. 6.

FIG. 8 is an enlarged cross-sectional view of an alternative base blockin another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well-known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

To facilitate discussion, FIG. 4 is a top view of a base block 400 usedin a preferred embodiment of the invention. The base block 400 comprisesa frame 404 and a porous block 408 mounted within the frame 404. FIG. 5is an enlarged view of part of the frame 404 and porous block 408. Theporous block 408 is defined as a block with a plurality of holes 412 onthe upper surface of the porous block 408. The holes 412 have a diameterin the range of 0.005 mm to 2.00 mm. More preferably, the holes 412 havea diameter in the range of 0.005 mm to 1.50 mm. Most preferably, theholes 412 have a diameter in the range of 0.005 mm to 0.200 mm. Thediameters of the holes 412 are set so that air passing through the holeswill have a some resistance and yet wide enough to allow a vacuumpressure to be applied through the holes. The density of the holes areat least 5 holes per square centimeter. More preferably, the density ofholes are at least 10 holes per square centimeter. Most preferably, thedensity of holes are at least 15 holes per square centimeter.Preferably, the ratio of the area of the holes to the area of theremainder of the upper surface of the porous block is at least 20%. Morepreferably, the ratio of the area of the holes to the area of theremainder of the upper surface of the porous block is at least 40%. Mostpreferably, the ratio of the area of the holes to the area of theremainder of the upper surface of the porous block is at least 60%.

FIG. 6 is a cross-sectional schematic view of the base block 400 beingused in a die attach and wire bonding device 600. The base block 400 ismounted on a vacuum device 604, which uses an exhaust fan 608 to createa vacuum across the bottom side of the porous block 408 of the baseblock 400. A heater 612 is thermally connected to the base block 400, sothat the heater 612 may heat the base block to temperatures on the orderof 150° C. A lead frame 620 mounted on lead frame base tape 624 isplaced on the top surface of the porous block 408 of the base block 400.A top clamp 628 may be used to help hold the lead frame 620 to the baseblock 400. In operation, the exhaust fan 608 and vacuum device 604create a vacuum on the bottom surface of the porous block 408 of thebase block 400. A further definition of the porous block 408 is that theporous block forms passageways between the holes on the top surface ofthe porous block 408 and the bottom surface of the porous block 408, sothat the vacuum applied to the bottom surface of the porous block 408generates a vacuum at the holes 412 (FIG. 5) at the top surface of theporous block 408. The vacuum is applied through the holes 412 (FIG. 5)to the lead frame base tape 610. Since the holes 412 are spaced to coverat least 60% of the surface of the base block 400, at least 50% of thelead frame base tape 624 connected to the die attach pad 632 will beheld by the vacuum from the holes 412. The base block may provide anevenly distributed vacuum across the surface of the lead frame 624,which may provide a better holding without movement than the prior art.In addition, if a different lead frame is used with a different dieattach pad, lead, and tie pattern the base block 400 would be able toprovide an improved hold with the different lead frame. This allows thebase block 400 to serve as a universal base block, which does not needto be changed when the lead frame pattern is changed.

A chip attaching device 640 is used to attach chips 644 to the dieattach pads 632. The chip attaching device 640 may use an epoxy 648 tomechanically connect the chips 644 to the die attach pads 632. Theheater 612 may then heat the base block 400 to about 150° C. A wirebonding device 652 may then be used to create wire bonds 656 between thechips 644 and leads of the lead frame 624. Heating the lead frame 624 toabout 150° C. may help during the wire bonding process.

The porous block 408 may be formed from any hard porous material on themarket, such as ceramic or stone. However, in the case where conductingheat from a heater to the lead frame is done through the porous block408, it is desirable to use a metal porous block. Such metal porousblocks may be naturally porous or a plurality of pin holes may be formedin the metal to form a metal porous block. FIG. 7 is an enlargedcross-sectional view of part of the base block shown in FIG. 6 in oneembodiment of the invention. The base block 400 comprises the frame 404and the porous block 408, which is shaded to indicate that the materialof the porous block 408 is porous. FIG. 8 is an enlarged cross-sectionalview of an alternative base block 800, which comprises a frame 804 and aporous block 808, which in this case is a solid block with a pluralityof pin holes 812 that have placed through the porous block 808. The pinholes 812 may be formed using lasers or mechanical drills or by othermethods. The pin holes may be in a uniform pattern or randomlydistributed, as long as the pin holes are within the diameter range,density range, and area ratio range as described above. The pin holes orporousness allow the holes to be in fluid contact with the vacuum device604.

In an alternative embodiment, especially if straight through pin holesare used, the base block may be made without a frame or the frame may beformed by outer walls of outer pin holes.

While this invention has been described in terms of several preferredembodiments, there are alterations, modifications, permutations, andsubstitute equivalents, which fall within the scope of this invention.It should also be noted that there are many alternative ways ofimplementing the methods and apparatuses of the present invention. It istherefore intended that the following appended claims be interpreted asincluding all such alterations, permutations, and substitute equivalentsas fall within the true spirit and scope of the present invention.

What is claimed is:
 1. A universal clamping device for processing leadframes of various shapes and sizes, comprising: a porous block with afirst side and a second side, wherein the porous block comprises aplurality of holes on the second side of the porous block, wherein adensity of the plurality of holes is at least 5 holes per squarecentimeter, wherein the first side of the porous block is the bottomside and the second side of the porous block is a top surface, andwherein the second side of the porous block is exposed to allow leadframes of various shapes and sizes to be placed on the second side ofthe porous block, so that the porous block may universally hold leadframes of various shapes and sizes; a vacuum system connected to thefirst side of the porous block; and a chip attaching device on thesecond side of the porous block, for attaching chips to lead frames ofvarious shapes and sizes.
 2. The device, as recited in claim 1, whereinthe diameter of each of the plurality of holes is less than 2.00 mm andwherein the plurality of holes are in fluid connection with the vacuumsystem.
 3. The device, as recited in claim 1, further comprising a wirebonding device on the second side of the porous block.
 4. The device, asrecited in claim 3, further comprising a heater connected to the firstside of the porous block.
 5. The device, as recited in claim 4, whereinthe plurality of holes have an area and the second side of the porousblock has an area wherein the area of the holes and the area of thesecond side of the porous block have a ratio, wherein the ratio of thearea of the holes to the area of the second side of the porous block isat least 20%.
 6. The device, as recited in claim 5, further comprising aclamp for clamping a lead frame to the second side of the porous block.7. The device, as recited in claim 1, further comprising a clamp forclamping a lead frame to the second side of the porous block.
 8. Thedevice, as recited in claim 7, wherein the porous block comprises aplurality of holes on the second side of the porous block wherein thediameter of each of the plurality of holes is between 0.005 mm to 0.200mm.
 9. A device for processing lead frames, comprising: a porous blockwith a first side and a second side, wherein the porous block comprisesa plurality of holes on the second side of the porous block, wherein thediameter of each of the plurality of holes is in the range of 0.005 mmto 2.00 mm; a vacuum system connected to the first side of the porousblock, wherein the plurality of holes on the second side of the porousblock are in fluid connection with the vacuum system; a heater connectedto the first side of the porous block; and a chip attaching device onthe second side of the porous block.
 10. The device as recited in claim9, wherein the first side of the porous block is the bottom side and thesecond side of the porous block is a top surface.
 11. The device, asrecited in claim 9, further comprising a wire bonding device on thesecond side of the porous block.
 12. The device, as recited in claim 9,further comprising a clamp for clamping a lead frame to the second sideof the porous block.
 13. The device, as recited in claim 9, wherein thesecond side of the porous block is exposed to allow lead frames ofvarious sizes and shapes to be placed on the second side of the porousblock, so that the porous block may universally hold lead frames ofvarious sizes and shapes.